The Sirius Mermaid
by NeonDomino
Summary: Based Loosely on The Little Mermaid. Merman Sirius wants nothing more than to walk on land and visit Hogwarts. After saving a human from the lake, he finally gets his chance to visit the castle and find the boy he's fallen in love with. Sirius finds himself faced with the challenge of getting the boy to return his love, so Sirius can make his legs permanent and get his voice back.


**Written for:**

 **50:50 Challenge** \- Prompts: Happily Ever After, AU: fairytale of your choice

 **OTP AU Challenge** \- Prompt: The Little Mermaid

 **Stratego** \- Word/Phrase/Object: Sirius' favourite hairband

 **Quidditch Pitch** \- Fish

 **Gringotts Prompt Bank** : Feeling: Miserable; AU: Fairytale!AU; Moist; Merperson; Impossible

 **Game of Life** : skirts, anchor

 **Ultimate Chocolate Frog Card Trading and Duelling Challenge** \- (Silver): Shrake:  Challenge: Incorporate someone fishing into your story.

 **Hogwarts School:** **Major and Minor Arcana:** For this lesson, I want you to consider the idea of 'bold action' in your story. This can be in terms of needing answers, embarking on a new path or anything else that requires someone to make a stand and do something. Maybe someone needs to know the truth about something so much they confront it head on, or have been waiting for so long for a relationship to start that it's time to jump right in. **Prompt:** [description] She/he set her jaw hard, knowing what he/she had to do." (Names can be substituted)

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 **So, I was trying to make this a one-shot, but it's turned into a MC because I can't seem to stop writing. It'll be about 3-5 chapters long.**

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 **The Sirius Mermaid**

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Sirius Black sat in his favourite spot beneath the ocean, examining his latest Human find. He carefully examined the thin elastic as he pulled at it, stretching it.

He had seen mostly the female Humans in skirts wearing these in their hair, and now he finally had one to add to his collection. It had to be his favourite part of his collection so far - it didn't matter that the object was simple, it was still valuable to him.

He slid down from the anchor, making his way to his cave, finding the mirror. He pulled out the hairbrush and began bringing it through his hair, although the water just messed his hair up again. Finally it was tidy, and Sirius used the elastic to tie a clumsy ponytail at the nape of his neck.

He smiled, admiring himself in the old mirror he had found, years ago.

Though the mirror showed him odd things. Not that Sirius would ever tell anyone what the mirror showed, or even show anyone of its existence.

He just found himself mesmerized by the sight that stared back at him. He watched in fascination as his tail slowly transformed, giving way to two very Human looking legs, clothing covering his body.

When he had spotted a Human with a leather jacket, the image changed, showing him wearing the exact same, as the more he watched the Humans on the surface, the more his image in the mirror seemed to change, reflecting what he wanted most.

To be up there, with them.

"Sirius!"

Sirius turned away from his mirror and towards the sound of his brother's voice. He slowly swam from the small cave, finding his brother not far from the entrance.

"Regulus?"

"Father sent me to find you. He has finished visiting with the Scottish Merfolk and we will be returning home first thing tomorrow. Come, it's quite late."

"Return home?" Sirius asked, dismayed. That meant leaving the mirror behind until next season, when they visited the Merfolk colonies again. "I'll follow you shortly."

Regulus frowned. "You're going up to the surface again, aren't you?" he asked. "Father told you that you weren't allowed up there again."

"And who is going to stop me?" Sirius asked. "I'm curious of their world."

"Well, it's not like you'll ever be part of it," Regulus muttered. He took in the longing expression in his brother's eyes. "Oh, Neptune! You want to be part of it."

"Is it too much to wish?" Sirius asked.

Regulus nodded. "You can't be part of that world. You can't even go close enough for a taste. Father and Mother would be furious. You have a tail, Sirius. They have those leg things. You live in water, they live on the land. There is no point wishing for the impossible."

Sirius sighed. "You're right," he agreed. "But I love looking at the castle in the distance. Can you allow me just a few minutes? It'll be the last evening I get to do so for a long time after all."

Regulus sighed, before nodding his head and turning back to the colony. Sirius watched him swimming away, before heading up to the surface to a rock that was almost directly above the anchor. He pulled himself onto the rock, and watched the castle.

It was getting dark, but that was the time he enjoyed the most - the castle was lit up and was so beautiful. His eyes moved over every inch he could see, and he lost himself in his favourite fantasy - visiting the towers. To walk across land and up the many stairs it would take to get there - it just sounded amazing.

He listened to the soft sounds of the water splashing against the rock, watching someone by the side of the water with a fishing rod. He hated those Humans that caught the beautiful fish that swam with him, and decided that he would go and mess with the hook. But before he could do anything, the boy had packed up and headed back to the castle. Distracted by him, Sirius failed to notice the two other figures at first. But it didn't take long for their voices to travel across the water, causing him to look around to find htem.

Sirius silently dove back into the water, moving closer, before stopping to peak out towards land.

The voices were angry, he determined. One Human was trying to walk away from the other, but the other Human was in his way.

Sirius had never a Human fight before, and slipped back under the water, moving even closer.

"I don't want any trouble, I just want to go back upstairs, and -"

"And pretend to be one of them?"

"I'm not pretending anything! I am a Human."

"If you were Human, you'd be able to stay in the castle during the full moon. You're just a filthy beast, Lupin."

"Please, Snape." Sirius watched the boy who had been trying to leave look around, his gaze darting to the lake, and he stayed completely still, hiding in the darkness of the lake.

"No wonder your father left. If I had a monster for a son, I'd have left too. I don't blame him."

Sirius watched in fascination as the slightly taller boy brought his arm back, letting it connect with the dark-haired Human's face, before storming off.

He watched the other one run up behind him, and the fight break out, ending with the dark-haired Human shoving the other Human into the lake, before turning and walking away.

But Sirius was the only one to see the boy's head smack against the rock, and Sirius had to break his father's rule - he had to let a Human see him. It was either that or let the Human drown, and Sirius wasn't like the sirens that took joy in singing and calling men or women into the water (even if he had the same power as those sirens). Humans were special, they needed to be protected!

Although the water was dark, Sirius knew exactly where he was going. He swam as fast as he could towards where he knew the boy would be.

He reached him quickly, and lifted the Human in his arms. As he pushed to get back to the surface quickly, he let his eyes fall on the Human's face, realising in shock just how beautiful this Human was. He reached the surface, getting as close to the land as possible and pushing the boy up.

With difficulty, he pushed the Human onto his side, only able to reach the Human's back to smack it hard, hoping to bring up some of the water he had possibly swallowed.

It wasn't long until the Headmaster was at his side. "Someone pushed him in and he hit his head," Sirius said, secretly thrilled that he was talking with a Human, and one that was so powerful. More powerful than his father, Sirius believed. He could sense the magic.

"Thank you," the Headmaster said, levitating the body, before offering Sirius a smile. "You're not from around here, are you?"

"We're visiting the colony," Sirius stated. His gaze fell on the castle. "What's in the towers?"

The Headmaster gazed at him thoughtfully for a moment. "A curious question," he murmured to himself. "The Common-rooms and Astronomy," he replied.

Sirius nodded, fascinated. "What is this place?"

"It's Hogwarts School of Witchcraft and Wizardry," Dumbledore explained patiently, though Sirius could see his eyes darting to the injured boy.

"And how did you know that he was hurt?"

"The wards informed me that a student was hurt out here. I was planning on using my wand to send a message, summoning one of the Merfolk to help retrieve him."

"One more thing," Sirius said. "Please don't tell my dad that I was on the surface. He'd curse me to Poseidon!"

"Of course," the Headmaster said, his eyes twinkling. "Thank you…"

"Sirius," Sirius replied.

"Thank you, Sirius," the Headmaster said, disappearing with the boy.

Sirius watched them go. It was a curse of fate that he found the Human boy to be much more beautiful than any of the Mermaids (or Mermen) that he had ever encountered. One he would never get to know, and one that he would probably never see again as he was leaving the next morning.

...oOo…

The morning came, and Sirius had consoled himself by thinking about how he would return the next year and maybe speak to his Human. The thought made him smile to himself. Maybe he could contact the Headmaster somehow and find out if his Human lived near the ocean… or a river or lake?

He was lost in his thoughts until his father approached him, demanding his attention. "One of the guards informed me that you were talking with the Human wizard," Orion said, getting straight to the point.

Sirius glared around at the Scottish Mermen, trying to pinpoint which guard had told on him. None would meet his eye and he turned back to his father.

"He said you brought a Human from the water and spoke with the Headmaster of the school."

"I only asked him about the castle," Sirius muttered.

"This colony may have an agreement with the Humans, but we do not," Orion stated, coldly. "It has been decided that you are not to return here again as you appear to be too familiar with Humans. You'll only visit with colonies that have no Human contact."

"No," Sirius said, looking at his father in despair. He couldn't tell his father about the beautiful Human he wanted to see again! "I won't stay away! What's so bad about Humans? I mean, I'd much rather be a Human than be a Merman!"

"His exclamation was met with silence, and Sirius' eyes widened as he realised his words. He knew his father would not take that statement well - especially with the colony watching.

"And what, pray tell, would make you think that?" Orion hissed, shifting closer to him.

"Because…" he hesitated, looking at his brother shaking his head from behind his father's back. "Because I… I met them."

"They are filthy creatures, polluting our water!"

"They aren't. They are special. And are so beautiful."

"Who is beautiful?" Orion narrowed his eyes at his eldest son.

"The Human I saved," Sirius admitted.

Orion moved so their faces were close together. "What did you say?" he whispered, allowing no-one else to hear the words.

There was no point denying it. "I said that I met a Human and he was beautiful."

"You're banned back to our castle," Orion hissed. "You have overstepped the boundaries by interacting with Humans, and have this disgusting notion that one could be beautiful. No son of mine is going to be allowed these thoughts -"

"Well…" Sirius began, feeling completely miserable, "maybe I don't want to be your son anymore."

With that, he swam away. Only Regulus chased after him.

...oOo…

Sirius had always been a faster swimmer, and he left Regulus in the distance, but two Merman caught up with him.

"Trying to stop me and bring me back to my father?" He snarled.

"Actually, we have a proposition for you," one of the Mermen stated.

"I don't want to hear it," Sirius said.

"Oh, you want to hear this," the other Merman said. "Let's just say… we know someone who can help."

"Help?" Sirius repeated, curiously.

"Well, you want to be Human, and she can make that happen."

"Make me Human?" Sirius murmured, thoughtfully. Could he really go through with that - become a Human, walk on land?

He didn't need to think for long - so many years he had dreamt of walking on land, and if there was any chance to get there.

"Who?" Sirius asked.

"Bellatrix, the sea-witch," a Merman replied.

From a distance, Regulus recognised his cousin's husband with Sirius and tried to swim faster - no good could come out of any deal she offered to him.

...oOo…

"So let me get this straight," Sirius said, looking at the contract on the table. "You'll give me legs - make me able to walk on land. Make me look like a male Human… and what do you get out of this?"

"Merely the happiness of my ickle cousin," Bellatrix replied, with a sickly-sweet smile. "But now that you mention it, I wanted one thing. I wanted your voice."

"My voice?" Sirius asked, carefully.

"It's not like you need it," Bellatrix stated. "You'll be on the land. I know, if you can make your Human fall in love with you and get him to kiss you, I'll give you your voice back and you can keep your legs too. Your voice can seduce anyone to fall in love with you, so I think it's best I take your voice. How does that sound?"

Sirius pictured the boy he had saved. He thought about how beautiful he was in the water, how light his body had been, and that someone had hurt him, and may even hurt him again. He considered the unkind words sent his way and nodded his head.

"Remember, once he declares his love for you, this is over. Now sign the agreement," Bellatrix insisted.

Sirius set his jaw hard, knowing what he had to do.

"Sirius, wait -" Regulus said, finally arriving and swimming over. "Don't do this!"

It was too late. A light hit Sirius in the centre of his chest, and his tail began to transform. He opened his mouth, but began to choke on the water.

With a shocked look at his cousin, Regulus grabbed Sirius under his arm and began to drag him up to the surface.

...oOo…

He was shoved onto his favourite rock, and Regulus began pounding on his back as Sirius knelt, coughing the water up. He gasped in the fresh air, finally calming down enough to breath properly.

That's when he realised he was kneeling. On his knees.

He slowly turned over, stretching the legs out in front of him. They were amazing, just like the Humans had. He poked at his foot, before moving his toes.

"Regulus," he tried to say, but no words left his mouth. He clutched at his throat, realising his voice was a larger loss than he had expected it to be.

Regulus just stared at him sadly. "Sirius," he whispered. "What have you done?"

Sirius just pointed gleefully at his new legs. After a moment, he pointed at his legs, and then at Regulus' tail, looking at him expectantly. There was a long silence and Sirius gestured between the both of them, pointing at his legs and at the castle.

"You… you want me to join you there?" Regulus asked, frowning as Sirius nodded.

"Sirius, I can't. My place is in the ocean and I'm happy in the water. I'm not like you, I have no desire at all to walk on land. The only reason I'm on the surface right now is because of you!"

Sirius pouted, miming putting a crown on his head and a ring on his finger.

"To take over ruling, and to wed a Mermaid," Regulus continued, with a slight smile. "Well, now with you out of the water, I won't have to compete. I can have any Mermaid I desire."

Sirius chuckled silently. He gestured to himself, held a hand over his heart and pointed at the castle.

"Your love is in there? Sirius, are you sure about this - that this is what you want? That it'll even work out?"

Sirius nodded twice, giving a small shake at the end.

"You're not sure if it'll work out?" Regulus replied.

Sirius repeated the motions to explain where his love was, slightly frustrated that he couldn't just tell his brother that he had to at least try.

"I'll convince father to let me stay here," Regulus said. "If you need me... I need to make sure you are okay."

Sirius leaned in to hug Regulus, patting his cheek fondly.

"I'll talk to one of the guards, get him to watch for you and to alert me. Father will be furious. Do you want help over there?"

Sirius shook his head. He was the strongest swimmer, after all. He didn't need Regulus.

"Good luck," Regulus whispered. Sirius moved to slide off the rock, but Regulus grabbed his arm. "Sirius, I don't mean to alarm you… but there's something weird between your legs. What the hell is that?"

Sirius looked down at the strange addition to his body, shrugging his shoulders. He was sure he'd find out soon enough. He touched his skin, realising that instead of feeling moist, it felt dry.

How did Humans manage with such dry skin?

...oOo…

Regulus deposited the coughing boy onto the ground, hesitating on whether to drag Sirius back over to the rock and think about what was happening, or getting his tail back somehow. Sirius hadn't even been able to swim from the rock to the land, which was shocking as Sirius had always been such an amazing swimmer.

"Sirius, are you sure?" Regulus said, as the coughing subsided.

Sirius nodded again, his eyes falling on the castle. His hand rested on his heart, and he pointed.

"What if he's not in there? What if you can't get him to fall for you - your power was in your voice, Sirius."

Sirius shot him a determined look, and Regulus had no doubt that Sirius would in fact get this Human to fall in love with him, voice or not.

"Good luck, brother," Regulus said, as an elderly wizard approached them.

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